1. Field of the Invention
The present invention relates to a subrack for pluggable printed circuit boards, with a screening or shielding housing in which a connecting backplane with backplane connectors for electrically connecting the printed circuit boards to one another and/or to other modules is arranged, and a printed circuit board from which an electric line is led out of the housing to an electrical connection in a fashion exhibiting EMC (electromagnetic compatibility).
2. Description of the Related Art
The German Patent Document DE-A-39 07 278 discloses a transfer system for electric signals in which printed circuit boards having electronic circuits arranged in on them are arranged parallel to one another in a screening housing. The cuboid housing is sealed by metal walls on five sides in a fashion exhibiting EMC (electromagnetic compatibility). Fitted on the end face of each printed circuit board is a metal front plate which directly adjoins a neighboring front plate or a side wall of the housing and is in metallic contact therewith. The juxtaposition of the front plates forms the sixth housing wall. An electrical connection, led out of the housing, of a printed circuit board is designed as a plug which penetrates the front plate.
The known arrangement ensures a sealing of the housing which exhibits EMC only if the sixth housing side is sealed without a gap by front plates or dummy elements. Leading the electrical connections out of the screening housing in a fashion exhibiting EMC is therefore already technically complicated and thus expensive because a special plate must be held in reserve for each type of plug used. Moreover, each printed circuit board must be provided with a front plate even if it has no electrical connection to the outside. Unassigned board slots for printed circuit boards must be sealed by a dummy element in the form of a front plate. Added to this are the contact strips on the longitudinal sides of the front plates and dummy elements which make the galvanic contact with the neighbor.
In the known transfer system for electric signals, connections are initially led from the data processing unit located in the screening housing to a backplane which separates the screening housing from the actual transfer space. However, depending on the type and number of the printed circuit boards used in a data processing unit and on the peripherals to be connected to the latter, the mounting of components therein can vary greatly. Thus, either it is necessary to provide the backplane with a number of plugs which are required for the maximum mounting of components in the data processing unit, which plugs must in addition have the maximum number of poles to be expected, or it is necessary to hold various backplanes in reserve for the different component mounting variants. Both solutions are impracticable because of the high costs alone.